The twenty first century may well be called an era of nanotechnology. For the last several decades, studies on nanotechnology have achieved excellent results, and more study results on and developments of nanotechnology are being expected.
Generally, nanomaterials refer to nanowires and nanorods having diameters ranging from less than 10 nm to several hundred nm.
Reliability evaluation methods and technologies for nanomaterials are necessarily required in an aspect of applications of nanotechnology, and accordingly a systematic mechanical property measuring and analyzing technology for nanomaterials needs to be developed.
As shown in FIG. 7, a mechanical property measuring apparatus for nanomaterials includes an electron microscope 100 for observing and controlling a nano material 35, a nano-manipulator 60 mounted within the electron microscope 100 to control the nanomaterial 35 and perform a mechanical property test, and a force sensor 1 having a cantilever shape and controlled by the nano-manipulator 60. Load values can be obtained by using the force sensor 1 during a mechanical property test, and the results are numericalized by a computer.
The nano-manipulator 60 is installed within a scanning electron microscope 100 to be driven in a vacuum state, in which a feed through for data communication between an interior of a vacuum chamber and the outside is installed to maintain a vacuum state.
Further, the nano-manipulator 60 realizes 3-axis control at a minimum resolution of 10 nm for a smooth experiment for the nanomaterial 35, and since the nano-manipulator 60 needs to be precisely driven along the axes, a motor which can be minutely driven while not generating electromagnetic fields, that is, a piezoelectric nanomotor is mounted to the nano-manipulator to perform precise control such as minute manipulation in nano unit.
As shown in FIG. 7, the nano-manipulator 60 is configured to linearly moved along the X, Y, and Z axes, and the force sensor 1 and a tungsten tip may be replaced in a sensor holder 2 connected to the Z axis.
The nano-manipulator 60 is mounted at an upper portion of an interior of a chamber of the electron microscope 100 so that a body or an attachment of the nano-manipulator 60 cannot cover a detector in charge of an image of the electron microscope 100 to badly influence the image.
Further, the nano-manipulator 60 is controlled by a keyboard of a computer or a joystick through a control box called network control (NWC).
Then, a maximum movement distance of the nano-manipulator 60 along the axes is 20 mm.
The force sensor 1 serves to measure a load applied to the nanomaterial 35 when a bending or tensile load is applied to the nanomaterial 35 to measure a mechanical property of the nanomaterial 35.
As shown in FIG. 7, the force sensor 1 is of a cantilever type having a shape similar to that of an AFM tip, and it is easy to bond the nanomaterial 35 to the body of the sensor by using an electron beam of the electron microscope 100 during a tension test.
The body of the force sensor 1 is formed of SiO2 and a piezoelectric material such as ZnO is applied on a SiO2 surface, so that an infinitesimal force is applied from the outside, an electrical change due to compression or tension applied to a thin film while the cantilever is bent is converted into a mechanical value.
Then, an accurate load value can be obtained during a mechanical property test for the nanomaterial 35 by inputting a natural spring constant K of SiO2 to perform a calibration.
As shown in FIG. 8, a natural spring constant of SiO2 varies according to a thickness of SiO2, a resolution of the force sensor 1 depends on the K value, an average resolution of the force sensor 1 is 100 nN or less, and a maximum of several mN can be measured.
FIG. 9 is a flowchart showing a method of testing a nano property according to a generally known mechanical property test procedure. First, the nanomaterial 35 in a powder state is dispersed, and then the nanomaterial 35 dispersed for a mechanical property test is selected by using the tungsten tip or the force sensor 1 and a location of the nanomaterial 35 is controlled.
If the nanomaterial 35 to be tested is determined, a tension or bending test is performed on the nanomaterial 35 after the nanomaterial 35 is gripped between the tungsten tip and the force sensor 1.
An electron beam of the electron microscope 100 is used to grip the nanomaterial 35 between the tungsten tip and the force sensor 1.
If the electron beam is scanned to a contact portion between the nano material 35 and the tungsten tip, carbon molecules and hydrocarbon molecules existing within the electron microscope 100 are deposited so that the nanomaterial 35 is gripped by the tungsten tip.
Then, if a gripping degree of the nanomaterial 35 is evaluated to be normal, tension and bending tests are performed, while if determined to be inferior, the nanomaterial 35 is wasted.
FIG. 10 is a picture showing an example of a tension/bending test for nanomaterials.
In order to perform a tension test for the nanomaterial 35, the nanomaterial 35 is made horizontal to an end of the force sensor 1 by vertically gripping the nanomaterial 35 by the tungsten tip or a rigid body and rotating the holder 2 of the electron microscope 100.
After the force sensor 1 and the nanomaterial 35 are horizontally positioned for an accurate measurement during the tension test, the force sensor 1 and an end of the nanomaterial 35 are gripped by using an electron beam of the electron microscope 100 and a tension test is performed on the nanomaterial 35.
According to the tension test method, the nano-manipulator 60 is adjusted by using a joystick, a tensile force is applied to the nanomaterial 35 gripped by an end of the force sensor 1 if the force sensor 1 is pulled by using the nano-manipulator 60, and the force sensor 1 converts an electrical change due to a tension applied to a piezoelectric material into a mechanical value.
Further, a mechanical property is evaluated by using a spring constant K of the force sensor 1.
The force sensor 1 is positioned on the right side of the nanomaterial 35 to perform a bending test on the nanomaterial 35, and the force sensor 1 and the nanomaterial are positioned perpendicular to each other for an accurate measurement.
Then, the nanomaterial 35 and the force sensor 1 are not gripped but a bending test is performed after a position of the force sensor 1 is determined.
According to the bending test method, the nano-manipulator 60 is adjusted by using a joystick, and the nanomaterial is deflected by moving the force sensor 1 by using the nano-manipulator 60.
The bending test is performed not until the nanomaterial 35 is fractured and within a range where a nonlinear section is not generated as the force sensor 1 and the nanomaterial 35 are slid with respect to each other.
If tests of mechanical properties, that is, tension and bending tests are performed on the nanomaterial 35 by using the nano-manipulator 60 and the force sensor 1 in this way, a displacement-load graph of FIG. 11 is obtained, a strain-stress graph can be obtained from FIG. 11, a modulus of elasticity of the nanomaterial 35 can be obtained from the strain-stress graph, and a tensile strength and a percentage of elongation of the nanomaterial 35 can be obtained
Thus, reliability of nanomaterials 35 can be evaluated and reliability of nano and micromaterials can be predicted by comprehending characteristics of nanomaterials 35 through mechanical property test using the nano-manipulator 40 and the force sensor 1 and creating a database for mechanical property test results on the nanomaterials 35, allowing mechanical property test services for various nanomaterials 35.
However, since only measurement of mechanical properties of nanomaterials 35 is given undue stress to the force sensor 1 according to the related art, a sensor capable of measuring a mechanical property and an electrical property at the same time is required.